For long-endurance stratospheric operations using airships, methods must be found to overcome the problems of leakage of lifting gas, degradation/failure of individual components and systems, and provision of energy for housekeeping, propulsion and station-keeping (if required for the mission) and payload operations. While it may be possible to rely on renewable energy sources for some missions (specifically, solar energy), the problems of leakage and component and subsystem degradation/failure remain. For truly long-endurance operations, which may extend indefinitely (i.e., which have no planned ending date or specific/finite mission duration), a way must be found to replenish lifting gas, replace or otherwise mitigate component and subsystem failures, and replenish fuel supplies (if the energy needs of the system are not fully accommodated by renewable sources such as solar energy).
Co-pending application Ser. No. 13/048,625 describes a tandem airship system which substantially reduces overall system cost, compared to traditional long-endurance stratospheric systems, by relying on a payload airship and a plurality of logistics airships. The payload airship can remain on-station indefinitely (barring failures) while it is sequentially tended by the plurality of logistics airships which provide, inter alia, power and station-keeping services. The logistics airships are cycled back-and-forth between a ground station (or stations) and the payload airship, as needed, as their consumables are depleted. A key factor affecting the depletion of consumables is the energy cost of propulsion needed for station-keeping.
Co-pending application Ser. No. 13/159,215 describes a tethered airship system which substantially reduces the energy cost of station-keeping (e.g., for long-endurance operations in the stratosphere) by relying on a tethered combination of two airships spaced far apart in altitude, such that the airships typically experience winds in opposite directions. However, the problem of gas leakage remains.
Co-pending application Ser. No. 13/227,966, entitled “Lifting Gas Replenishment in a Tethered Airship System,” filed Sep. 8, 2011, describes a gas replenishment method and apparatus that can be used within the context of the tethered airship system previously disclosed, thereby overcoming the problem of gas leakage for the upper airship. However, this system relies on a gas reservoir on the lower airship. Eventually, this gas reservoir will become depleted.
Co-pending application Ser. Nos. 13/048,625, 13/159,215, and 13/227,966, are fully incorporated herein by reference. However, in this disclosure, unless explicitly stated otherwise, the term “mating” is assumed to also encompass the concept of “docking”.
This invention is directed to the problem of long-endurance and open-ended (with respect to time) stratospheric missions, although the invention may find other applications. It combines a tethered airship system with gas replenishment, as described in Ser. Nos. 13/159,215 and 13/227,966, with a tandem support concept as described in Ser. No. 13/048,625, to provide for replenishment of lifting gas and fuel (if required) from the ground, replacement of failed subsystems/components, station-keeping, and shuttle of payloads to/from a mission area.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.